1. Field of the Invention
The present invention relates to a level adjustment device which adjusts the level of an acoustic signal and, in particular, to a level adjustment device which is suitable for level adjustment when an analog acoustic signal is input to an acoustic signal processing apparatus, such as a digital mixer.
2. Background Art
In an acoustic signal processing apparatus, such as a digital mixer, an amplifier is provided in an input section of an analog acoustic signal to adjust the gain. The amplifier is configured to adjust the level of an input analog acoustic signal in accordance with a manipulation of a user.
The reason for the adjustment is that an acoustic signal input from an analog input terminal has various amplitude levels depending on what type of apparatus is used as a generation source, and the level balance of the acoustic signal is arranged such that all the amplitude levels are optimally handled in the acoustic signal processing of the acoustic signal processing apparatus.
In realizing the level adjustment function, an attenuator, called a pad, is provided in front of the amplifier to attenuate the amplitude level of the acoustic signal by a fixed value.
With the use of the pad, the range of level adjustment in the level adjustment function can be increased further than an adjustment range which can be realized by only the amplifier.
For example, if the adjustment range of the amplifier is +16 dB (decibel) to +60 dB, and the attenuation amount of the pad is −26 dB, when the pad is off and only the amplifier is used, adjustment can be done from +16 dB to +60 dB. Meanwhile, when the pad is on and the amplifier and the pad are used in combination, adjustment can be done from −10 dB to +34 dB. As a whole, the adjustment range from −10 dB to +60 dB can be obtained.
This level adjustment device is described in, for example, JP-A-2008-263410 (the paragraph 0019 and FIG. 1), “PM5D/PM5D-RHV2/DSP5D Manual”, Yamaha Corporation, 2004 (specifically, p. 43), and “DM2000 Version2 Manual”, Yamaha Corporation, 2004 (specifically, p. 64)
However, in manipulating the above-described level adjustment device including the pad and the amplifier, in “PM5D/PM5D-RHV2/DSP5D Manual” and “DM2000 Version2 Manual”, the user manually manipulates the on/off of the pad. In this case, in performing level adjustment, two types of manipulation including the setting of the amplifier gain and the setting of pad on/off are necessary. Thus, there is a problem in that it takes a lot of effort to carry out the manipulation.
In order to solve this problem, a configuration is considered in which a switching point is provided such that the on/off of the pad is automatically switched. That is, a configuration is considered in which, when the level adjustment value received from the user is greater than the switching point, the pad is off and level adjustment is performed by only the amplifier, and when the level adjustment value is smaller than the switching point, the pad is on and then the pad and the amplifier are used in combination to perform level adjustment. In general, in switching the on/off of the pad, noise is generated, the acoustic signal becomes mute.
On the other hand, in the level adjustment device, level adjustment may be performed such that the level adjustment value is raised and falls finely within a limited range. In the above-described configuration in which the switching point is provided, if such level adjustment is performed, when level adjustment which raises and falls the level adjustment value finely is performed near the switching point, the on/off of the pad is switched each time the level adjustment value passes through the switching point. Accordingly, there is a problem in that mute is frequently generated, and the acoustic signal is frequently discontinued, causing an undesirable state.